Effect of electric field on the rheological and dielectric properties of a liquid crystal exhibiting nematic-to-smectic-A phase transition

• Published in: The European physical journal. E, Soft matter and biological physics Soft matter and biological physics, 2011-08, Vol.34 (8), p.74-74, Article 74
• Main Authors: Ananthaiah, J., Rajeswari, M., Sastry, V. S. S., Dabrowski, R., Dhara, S.
• Format: Article
• Language: English
• Subjects: Biological and Medical Physics; Biophysics; Complex Fluids and Microfluidics; Complex Systems; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Nanotechnology; Physics; Physics and Astronomy; Polymer Sciences; Regular Article; Rheology; Soft and Granular Matter; Specific phase transitions; Surfaces and Interfaces; Techniques and apparatus; Thin Films; Transitions in liquid crystals; Viscosity measurements
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/i2011-11074-y

We report simultaneous measurements of shear viscosity ( η ) and dielectric constant ( ε ) of octyloxy cyanobiphenyl (8OCB) in the nematic (N) and smectic-A (SmA) phases as functions of temperature and electric field. With increasing electric field η increases in the N phase whereas it decreases in the SmA phase and saturates beyond a particular field in both the phases. The flow curves in the intermediate-field range show two Newtonian regimes in the N phase. The temperature-dependent behavior of η and ε at zero or at small electric field suggests the occurrence of several structures that results from precessional motion of the director along the neutral direction as reported in similar other system. We show that the precessional motions are gradually suppressed with increasing electric field and the effective viscosity resembles with the Miesowicz viscosity η 1 at high enough electric field. In the intermediate field range the temperature-dependent η exhibits anomalous behavior across the N-SmA phase transition which is attributed to the large contribution of Leslie coefficient α 1 .